1. Field of the Invention
The present invention relates to an inkjet recording apparatus and a control method of an inkjet recording apparatus, and more particularly to an inkjet recording apparatus and a control method of an inkjet recording apparatus that record images using invisible ink.
2. Description of the Related Art
There have been widely known an inkjet type recording apparatus (hereinafter referred to as “inkjet recording apparatus”) as a recording apparatus that can correspond to the demand of small quantity and various kinds of recording suited to the occasion. Inkjet recording apparatuses generally jet droplets of ink from nozzles formed on a recording head at the surface facing a recording medium, land and fix the ink on the recording medium to record images on the medium. The inkjet recording apparatus differs from image recording method used in a conventional gravure printing method or flexography printing method, and has such a feature that it can correspond to the demand of small quantity printing easily and speedily because it does not need a plate making process. Further, the inkjet recording apparatus has such an advantage that it has a low noise level and can record colored images easily by using multi-color inks.
Recently, there has been also known an inkjet recording apparatus that uses photo-curable ink, as an inkjet recording apparatus that can deal with various kinds of recording mediums (refer to, for example, Japanese Non-examined Patent Publication, JP-Tokukai-2001-310454A). This type of inkjet recording apparatus jets droplets of photo-curable ink containing a photo-initiator having a predetermined sensitivity to light such as ultraviolet rays, irradiates the ink deposited on a recording medium to cure and fix the ink on the medium. This type of inkjet recording apparatus rapidly cures the ink by irradiation of light after landing of ink droplets, therefore prevents the ink from soaking or bleeding in the recording medium. This characteristic allows image recording not only on plain paper but also on a recording medium made of plastic or metal that does not have an ink-receiving layer and does not absorb ink at all.
Among such inkjet recording apparatuses, a serial-type inkjet recording apparatus, while reciprocating recording heads and light irradiating devices in a width direction of the recording medium, the recording heads jet ink droplets and the light irradiating devices irradiate the deposited ink to fix the ink on the medium. Because the time from jetting of ink from a recording head to irradiation of light varies according to the forward and backward movement in the reciprocating movement, there occurs a difference in a color tone and gloss of recorded images in the main scanning direction due to the variation in dot sizes and dot-connection states. For solving this problem, there has been known such a technology that the degree of dot overlap does not vary in both forward and backward directions in the main scanning direction, by disposing two sets of recording heads, which jet droplets of plural color inks, symmetrically in the main scanning direction (refer, for example, to JP-3248704B).
There has been also known such a technology that jetting amount of ink is adjusted according to ink penetrance into a recording medium in an inkjet recording apparatus that uses water-base ink for recording images (refer, for example, to JP-Tokukai-2003-25613A).
Further, there are sometimes found variation of images, unevenness due to difference in applied ink quantity, partial excessive gloss, etc. in a case that photo-curable ink is used. These irregularities are obviously found in the recorded area where large quantity of ink is applied. The reason for these irregularities is considered as follows. When water-base ink or oil-base ink is used for recording, most of ink is absorbed into a recording medium, but when photo-curable ink is used, the ink remains on the recording medium and is cured with the ink-deposited portion protruded, which produces an uneven surface of the recorded images due to variation of the deposited ink quantity.
For solving this problem, such an inkjet recording apparatus is disclosed that, by using two types of inks, one containing a coloring material (hereinafter, “color ink”) and the other containing no coloring material (hereinafter, “invisible ink”), images are recorded so that both types of inks are deposited on the recording medium with uniform volume in total (refer, for example, to JP-2003-191601A). Use of such inkjet recording apparatus permits a uniformly deposited ink quantity per unit area, thereby suppressing uneven gloss caused by variation of ink quantity, and improving the durability of the recorded images with the recording medium covered by the invisible ink.
However, the technology described in JP-3248704B needs to mount twice as many recording heads as usual one, thereby making an apparatus larger in size and increased in weight.
The technology described in JP-Tokukai-2003-25613A requires adjustment of jetting amount of ink according to the ink penetrance when using the water-base ink that permeates into a recording medium, and is not applicable to photo-curable ink that is hard to permeate into the recording medium, and that the size and connection state of ink dots are affected by a variation in curing timing by irradiation of light and by the intensity of irradiated light.
The technology described in JP-Tokukai-2003-191601A can obtain a certain level of uniform gloss in recorded images, but cannot obtain a desired level of uniform gloss, that is, cannot determine a jetting amount of invisible ink to realize the desired level of gloss.
In the serial-type inkjet recording apparatus using photo-curable ink, the time from landing of invisible ink to the light irradiation in a bidirectional scanning varies according to the forward and backward movements along the main scanning direction, thus leading to a problem that uneven gloss occurs caused by the uneven dot sizes of invisible ink.